Remove s3_cli module from test_utils

[rtyler]

In rust/src/test_utils.rs we have some shell invocations of the AWS cli which aren't necessary (IMHO) because we can do all of these operations directly from Rusoto without adding the system dependency.

[marijncv]

Hey @rtyler, I started taking a look at this issue and I'm wondering if it's going in the right direction with my draft PR #1570.

For now just creating the bucket with rusoto_s3 using their async API, but it required me to make a lot more functions async as well. Is that an issue? Or is there perhaps a better way of doing it? Curious for your feedback!

Edit: 0f015aa uses futures::executor::block_on() to deal with the async API of rusoto_s3 as an alternative to the approach of making more functions asyc, but it requires the tests that use it to have the #[tokio::test(flavor = "multi_thread")] macro